The present disclosure relates to devices and systems to address stability and vibration issues associated with high-speed rotating turbomachinery. More particularly, the present disclosure relates to devices and systems for addressing stability and vibration issues associated with gas turbine engines used in aircrafts, for example.
In gas turbine engines, maintaining operational clearances between the tips of rotating blades and the engine static structure and controlling vibration generated by the high speed rotating components are design critical factors in gas turbine engine development. Maintaining operational clearances between the tips of rotating blades and the static structure of the engine to reduce air leakage past the rotating blades impacts the thermodynamic efficiency and specific fuel consumption (SFC) of the engine.
Further, gas turbine engine shaft dynamics are critical, including the placement of shaft critical speed in the optimal frequency range and the rotor response to imbalance and transient excursions through critical speeds. The critical speed is usually controlled by adjusting the stiffness/flexibility of various components of the gas turbine engine, such as, for example, the shaft or shafts, the bearings, and the support structures. Moreover, rotating shafts in gas turbine engines can become abnormally unbalanced while operating. For example, a high pressure turbine shaft can become abnormally unbalanced after a turbine blade failure.
Shaft response to imbalance and transient critical speed operation (i.e., vibration response) are controlled via damping. In gas turbine engines, damping and stiffness control are typically achieved using hydraulic devices such as squeeze film dampers (SFD). In a gas turbine engine, the SFDs work in conjunction with and are typically contiguous with the various bearing systems that support the rotating shafts of the engine. A squeeze film damper achieves both stiffness and damping by virtue of the whirl motion of the shaft acting on the oil filled annulus (cavity) of the SFD.
However, both the stiffness and the damping coefficient achieved by typical SFDs are non-linear with respect to the orbital displacement of the shaft. Also, the stiffness and damping coefficients are linked such that a modification to one impacts the other. Because current SFD systems do not provide for variable control during operation, they are not able to precisely locate and control response to critical speeds, since stiffness and damping are varied along with whirl displacement. Thus, a SFD/bearing assembly is designed to cover the widest range of operating conditions for a particular engine.
A SFD that offers varied control would provide improved rotor tip clearance control during maneuver loading situations by limiting how far the bearing can move radially. Further, varied control damping will help keep tip clearances tight and reduce air leakage past the rotor blades resulting in improved specific fuel consumption. There remains a need to improve sealing of the SFD cavity to improve the reliability and consistency of the damping characteristics of the SFD system.